Maintenance of an old but very good Amplifier

A typical maintenance job on an old Hifi amp would involve the following:

• Safety First: Unplug the amp from the mains before removing the cover!
• Dust: Use a brush and a vacuum cleaner to remove dust. Some people would use compressed air, but I tend to disagree - compressed air often blows dust into nooks and crannies where it will be more difficult to remove.
• Crackles, Pops, an Intermittents: Clean switches and pots with a good contact cleaner. I recommend Kontakt 60. Don't use any cheap, off brand contact cleaner - it may do more harm than good. DO NOT USE WD-40!!! Apply the contact cleaner very sparingly spraying it into pots and switches through the small openings in their covers. Exercise the controls by briskly turning them from one end stop to the other several times (for pots and rotary switches) or pushing/flipping them a number of times in quick succession (toggles and pushbuttons). Some pots and switches are sealed and cannot be cleaned. Exercising them a bit usually clears any problems they might have. Note many amps have rotary selectors that are actually slide switches located on a circuit board distant from the front panel and actuated by a flexible strip that works a bit like a Bowden cable. If the amp has a headphone socket, spray a bit of contact cleaner into it and insert/remove a headphone plug a few times.
• Caps: Leave them alone unless there are obvious problems. I know recapping is all the rage these days, but I notice most caps in vintage hifi amps hold up surprisingly well.
• Signal connectors: The RCA type connectors on the rear panel can be effectively cleaned by wetting them with a drop of contact cleaner, inserting a loose plug and turning the plug back and forth a quarter turn a few times.
• Adjustment: Bias current and DC offset may drift over time, but adjustment should be left to a qualified technician. Misadjustment might blow up your amp, so leave those trim pots alone! If the amp makes a loud-ish thump on your speakers when you turn it on or runs hot when idle, have it checked. Except if the amp is advertised as being Class A (usually written on the front panel), 'cause Class A amps do run hot just sittin' there doin' nothing.

Here's a 1975 vintage Sony TA-1140 getting a tune-up: